This invention relates generally to fastening devices for securing two closure members together wherein the components of the fastener are retained in the respective closure members. More specifically, this invention relates to captive fasteners of the screw or threaded type.
Many types of captive fasteners are generally known in the art. Captive fasteners derive their name from the observation that the components of the fastener are retained, or "captivated", in the respective closure members. These fasteners are generally considered desirable because they prevent the loss of parts when the fastener is disassembled and also because they facilitate the reassembly of the fastener. Captive fasteners are particularly desirable for use in situations where access to one of the components of the fastener is difficult or impossible once the closure members are brought together.
One type of captive fastener that has been found particularly useful is the screw or threaded type which essentially consists of a male threaded member, such as a screw or bolt, and a female threaded member, such as a nut. This type of captive fastener is widely used on access panels for electrical and mechanical equipment which are periodically removed for purposes of inspection, adjustment, or repair. Typically, the screw component is retained by the access panel and the nut component is retained in the frame of the panel opening and is fixed against rotation so that no tool is required at that end of the fastener.
The screw component of known captive screw fasteners may be loosely retained in the panel or may be driven axially by means of a threaded component secured to the access panel. In the first mentioned arrangement, the screw component often protrudes from the inside surface of the panel when the panel is removed. The protruding screws are disadvantageous in that they often catch on clothing, wires, or the like and thus interfere with the removal and replacement of the panel. Another disadvantage of this arrangement is that the head of the screw often protrudes from the outside surface of the panel when it is assembled and thus prevents a flush panel surface when such an appearance is necessary or otherwise desirable.
In the other arrangement, that is, where the screw component is driven axially by means of a threaded member, difficulties arise in the installation and operation of the fastener. The difficulties in operation are due to the binding effect that occurs when the threads of the screw do not precisely align with the threads of the nut. This phenomenon is perhaps best observed by attempting to thread a screw through two separate nuts simultaneously. Unless the threads of the second nut are exactly aligned wit the threads of the first nut to form a continuous threaded helix, the screw threads will not mate properly with the threads of the second nut, and binding will occur.
In order to eliminate the binding effect in such an arrangement, the nut component of he fastener must be installed in the frame in a precise orientation to form a continuous threaded helix. Obviously, this precise installation of the nut component requires considerable skill and is thus time consuming and costly.